Schisandrin B, a dual positive allosteric modulator of GABA_A and glycine receptors, alleviates seizures in multiple mouse models

Epilepsy is a prevalent and severe neurological disorder and approximately 30% of patients are resistant to existing medications. It is of utmost importance to develop alternative therapies to treat epilepsy. Schisandrin B (SchB) is a major bioactive constituent of Schisandra chinensis (Turcz.) Baill and has multiple neuroprotective effects, sedative and hypnotic activities. In this study, we investigated the antiseizure effect of SchB in various mouse models of seizure and explored the underlying mechanisms. Pentylenetetrazole (PTZ), strychnine (STR), and pilocarpine-induced mouse seizure models were established. We showed that injection of SchB (10, 30, 60 mg/kg, i.p.) dose-dependently delayed the onset of generalized tonic-clonic seizures (GTCS), reduced the incidence of GTCS and mortality in PTZ and STR models. Meanwhile, injection of SchB (30 mg/kg, i.p.) exhibited therapeutic potential in pilocarpine-induced status epilepticus model, which was considered as a drug-resistant model. In whole-cell recording from CHO/HEK-239 cells stably expressing recombinant human GABA_A receptors (GABA_ARs) and glycine receptors (GlyRs) and cultured hippocampal neurons, co-application of SchB dose-dependently enhanced GABA or glycine-induced current with EC₅₀ values at around 5 μM, and application of SchB (10 μM) alone did not activate the channels in the absence of GABA or glycine. Furthermore, SchB (10 μM) eliminated both PTZ-induced inhibition on GABA-induced current (I_GABA) and strychnine (STR)-induced inhibition on glycine-induced current (I_glycine). Moreover, SchB (10 μM) efficiently rescued the impaired GABA_ARs associated with genetic epilepsies. In addition, the homologous mutants in both GlyRs-α1(S267Q) and GABA_ARs-α1(S297Q)β2(N289S)γ2L receptors by site-directed mutagenesis tests abolished SchB-induced potentiation of I_GABA and I_glycine. In conclusion, we have identified SchB as a natural positive allosteric modulator of GABA_ARs and GlyRs, supporting its potential as alternative therapies for epilepsy.